The invention concerns an oil-sealed vane-type rotary vacuum pump with an oil pump whose suction chamber is fitted with feeds for oil and gas. By loading the oil with gas, preferably with air, a reduction in the noise levels is attained when the vacuum pump is operating.
A vane-type rotary vacuum pump having the characteristics of the features of patent claim 1 is known from DE-A-3922417. The feed lines for gas and oil leading into the suction chamber of the oil pump according to the state-of-the-art are so arranged, that the oil pump will initially only pump air and then only oil. This is attained by designing the distance between the intake openings for air on the one hand and for oil on the other hand to be so great, that the intake opening for the oil is opened after the vane which follows next has already separated the circulating swept volume from the air intake opening. Simultaneous suction of air and oil is not possible. The known solution thus requires the use of an oil pump having at least three vanes which are arranged evenly spaced along its circumference. Only this ensures that oil will be sucked in also while the pump is running up. Without a supply of oil, both the oil pump and also the vane-type rotary vacuum pump which is to be supplied with oil would be damaged after a short time. A vane-type oil pump with three vanes is involved and thus costly. Moreover, the quantity of the air or quantity of the oil which is sucked in may only be influenced with the aid of nozzles with the risk that these might block.
From EU-A-474066 it is known to mix--in an oil pump which is also of the vane type--the supplied gas and oil before it enters into the oil pump. A Venturi nozzle is used for this. In the area of the Venturi nozzle the air flow and the oil flow run in parallel. Thus a pressure drop is created so that the oil is entrained with the gases. This solution too, is engineering wise relatively involved in particular because the use of a Venturi nozzle.